As semiconductor devices are becoming highly integrated, sizes of source/drain regions and width of gate electrodes and metal wiring in semiconductor devices are being decreased. Thus, multi-layered wirings have been used as a wiring structure of the semiconductor device in which a number of wiring layers are sequentially stacked in a vertical direction and each of the wiring layers are electrically connected to each other by interconnections such as a contact plug.
In general, the wirings in a semiconductor device can be electrically connected to underlying conductive structures such as transistors and are separated from each other by a number of insulation inter-layers. The insulated upper and lower wirings can be electrically connected to each other by the interconnections penetrating through the insulation interlayer. The interconnections may be a metal having low electrical resistance such as aluminum (Al), copper (Cu) and tungsten (W) as the high integration degree of the semiconductor device. Particularly, tungsten (W) has been used for the interconnection due to the quality of step coverage and high pattern facilitation provided.
Metals are generally formed into the wiring structure for a semiconductor device by a deposition process and the deposition process through chemical reactions at a high temperature. Thus, while performing the deposition process, various barrier layers can be provided between the insulation interlayer and the interconnection for preventing the damage to the insulation interlayer and the underlying conductive structures.
Tungsten (W) may have relatively low adherence to the insulation interlayer formed of, for example, an oxide. In addition, tungsten source gases in the deposition process can cause damage to sidewalls of a contact hole or a via-hole. For those reasons, the barrier layer usually includes a glue layer for compensating the adherence to the insulation interlayer and an anti-diffusion layer for reducing the diffusion of fluorine ions (F—), which can be byproducts of the fluorine source gases of the deposition process, into the insulation interlayer. For example, a multilayered structure of titanium and titanium nitride (Ti/TiN), tungsten and tungsten nitride (W/WN) or tantalum and tantalum nitride (Ta/TaN) is sometimes used as the barrier layer. Recently, W/WN structure is also used as the barrier layer because a tungsten (W) plug can be formed continuously with the W/WN barrier layer and electrical resistance between the barrier layer and the contact plug can be reduced.
Various deposition processes based on chemical reactions of source materials have been utilized for forming the WN layer that is conformal with the profile of the contact hole or the via hole and has high quality of step coverage. In such a case, problems may arise in that the contact resistance between the contact plug and a conductive structure underlying the contact plug may be unstable due to rapid temperature variation in the deposition process. Particularly, when copper (Cu) wirings are arranged under the contact plug, random electron migration may be generated on a surface of the copper wiring and thus a plurality of voids may be formed in the copper wirings to thereby increase the contact resistance between the copper wirings and the contact plugs.